The present invention relates generally to recording of a frequency-multiplex signal, and more particularly to a method and apparatus for recording on a recording medium a frequency-multiplex signal comprising components corresponding to a plurality of signals.
One known way of recording a frequency-multiplex signal involves, as illustrated in FIG. 1A, an adder for merely effecting the addition with respect to a plurality of signals having different frequencies so as to produce a frequency-multiplex signal which is in turn recorded on a recording medium. That is, in FIG. 1A, an adder 7 is responsive to a first signal S1 supplied through an input terminal 1 and a second signal S2 led through an input terminal 2 so as to produce a frequency-multiplex signal corresponding to the addition signal of the first and second signals S1 and S2, the first signal S1 having a frequency of f1 and the second signal S2 having a frequency of f2 which is lower than f1 as illustrated in FIG. 1B. After being amplified by a recording amplifier 4, the produced frequency-multiplex signal is recorded on a recording medium 6 through a recording device such as a magnetic head 5. In case of a magnetic recording/reproduction system, a recording signal current having a waveform (envelopes indicated by heavy solid lines) as exemplarily shown in (c) of FIG. 2 is fed to the magnetic head 5, and the recording is performed on the recording medium 6. Components of the first signal S1 and the second signal S2 in the frequency-multiplex recording signal current fed to the magnetic head 5 are illustrated in (a) and (b) of FIG. 2, respectively.
One problem faced in a recording/reproduction system having a non-linear chanracteristic is generation of an intermodulation distortion in the recording/reproduction signal. More specifically, after recording of a frequency-multiplex signal produced by a first signal with a frequency of f1 and a second signal with a frequency of f2, the reproduction signal reproduced by a recording/reproduction system having a non-linear characteristic includes the first and second signals and further includes spurious signals whose frequencies are mf1.+-.nf2 where m and n designate integers, respectively. The introduction of the spurious signals due to the intermodulation distortion causes deterioration of the reproduction signal, thereby resulting in reproduction of a distorted signal as exemplified in (d) of FIG. 2 in correspondance with the recorded frequency-multiplex signal illustrated in (c) of FIG. 2.